In order to deal with the demands of energy conservation and carbon reduction in recent years, the automobile industry is committed to reduce the weights of automobile bodies, so as to reduce fuel consumption to achieve the purposes of energy conservation and carbon reduction.
A conventional effective way to reduce the weights of automobile bodies is to thin thicknesses of steels used in automobile bodies; however, safety of the automobile bodies cannot be sacrificed during thicknesses thinning of the steels. Therefore, it is necessary to further enhance strength and ductility of the steels used in automobiles.
Over the past few years, the steel industry has developed the so-called 1st generation and 2nd generation advanced high strength steels (AHSSs). The 1st generation AHSSs mainly refer to transformation induced plasticity (TRIP) steels, the tensile strength thereof is about between 600 MPa and 1000 MPa, the elongation thereof is between 20% and 40%, and the strength-elongation product (i.e., the product of the tensile strength and the elongation) is less than 20 GPa %. Because the tensile strength and the elongation of the TRIP steels are lower than those required in the automobile industry, development of the 2nd generation AHSSs emerges.
The 2nd generation AHSSs mainly refer to twinning induced plasticity (TWIP) steels, which belong to high manganese alloy steels, and the manganese content is about between 20 wt % and 30 wt %. The TWIP steels have excellent strength, the tensile strength thereof is about between 600 MPa and 1100 MPa, and the elongation thereof can be maintained between 60% and 95%, so that the strength-elongation product can be up to 60 GPa %. Although the TWIP steels have developed for nearly ten years, a main reason why the TWIP steels still fail to be accepted by the automobile industry is that the TWIP steels require high manganese content and do not conform to consideration of commercial cost.
To sum up, because the strength-elongation product of the 1st generation AHSSs is too low to meet the requirements for properties of the steels used in automobiles and the manganese alloy content of the 2nd generation AHSSs is too high to meet commercial requirements, the automobile industry has turned to development of 3rd generation AHSSs.
Referring to FIG. 1, which shows a diagram of a location range of target zones of properties of the 3rd generation AHSSs. As shown in FIG. 1, the strength-elongation product of the 3rd generation AHSSs ranges about from 30 GPa % to 50 GPa %.
However, in the automobile industry, a method for manufacturing the 3rd generation AHSSs is still under development. Therefore, it is necessary to provide a method for manufacturing a high-strength and high-ductility steel to manufacture steels in line with or superior to the requirements for properties of the 3rd generation AHSSs.